The invention relates to a low-pressure discharge lamp provided with a radiation-transmitting discharge vessel which encloses a discharge space containing an ionizable filling in a gastight manner, and comprising electrodes arranged in the discharge space between which a discharge path extends, while at least one of the electrodes comprises a sintered mixture of metal and ceramic material, the proportional quantity of metal in the mixture being small in relation to the proportional quantity of ceramic material.
Such a lamp is known from German Patent 529 392. The known lamp has electrodes sintered from a mixture of a metal, such as W or Mo, and a ceramic material, such as an oxide or a silicate of an alkali metal, an alkaline earth, or a rare earth, the proportional quantity of metal being small compared with the quantity of ceramic material. The use of such electrodes has the advantage that a high current density is possible, so that the electrode can be comparatively thin, if so desired. This is of particular importance for lamps having comparatively narrow discharge vessels.
Ceramic materials are comparatively prone to fracture in the case of abrupt temperature changes. Such temperature changes may occur in the electrodes upon switching-on of discharge lamps. The presence of metal, which is comparatively ductile, can considerably increase the resistance to such temperature changes, provided it is present in the ceramic material in a sufficiently continuous structure. The continuity of the metal, however, decreases with a decreasing proportional volume of the metal.